1. Field of the Invention
The present invention relates to a synchronized X-ray or gamma-ray and high peak power, coherent terahertz source, and more particularly to a picoseconds laser-electron system for X-ray and T-ray screening and imaging of personnel, baggage and cargo containers.
2. Description of the Prior Art
X-rays and T-rays represent two kinds of radiation with wavelengths that are extremely short (less than a fraction of angstrom for X-rays and gamma-rays) and very long (fraction of millimeters for terahertz).
X-ray sources have been known for more than a hundred years and are widely used in medicine for imaging, diagnostics and therapy; in physics, biology and chemistry, and in other sciences and technologies including the semiconductor industry. A wide range of different X-ray and Gamma-ray devices and facilities are currently in operation: radiographic sources using radioactive isotypes (such as Co-60), classical vacuum High-Voltage (HV) tubes, various linear and circular accelerators that use Bremstrahlung radiation from a high-mass target like tungsten, synchrotron electron storage rings that produce high-brightness X-ray radiation from bending magnets and wigglers, backscattering Compton sources that produce high-brilliance X- and gamma-radiations by colliding energetic electron beams with coherent, intense flux of photons generated by lasers (including Free Electron Lasers or FELs), and super radiant FELs that use Self-Amplified Spontaneous Emission (SASE) of multi-GeV electron beam self-bunched in a very long undulator (e.g., about 100 m undulator in the LCLS FEL at SLAC). In the last three decades there have been advanced research, studies and applications using short-pulse, high-peak-brightness X-ray radiation produced in storage rings and synchrotrons.
X-ray sources have been known for more than a hundred years and are widely used in medicine for imaging, diagnostics and therapy, in physics, biology and chemistry, and in other sciences and technologies including the semiconductor industry. A wide range of different X- and Gamma-ray devices and facilities are operating: radiographic sources using radioactive isotopes (such as Co-60), classical vacuum High-Voltage (HV) tubes, various linear and circular accelerators that use Bremstrahlung radiation from a high-mass target like tungsten, synchrotron electron storage rings that produce high-brightness X-ray radiation from bending magnets and wigglers, backscattering Compton sources that produce high-brilliance X- and Gamma-radiations by colliding energetic electron beams with coherent, intense flux of photons generated by lasers (including Free Electron Lasers or FELS), and superradiant FELs that use Self-Amplified Spontaneous Emission (SASE) of multi-GeV electron beam self-bunched in a very long undulator (e.g., about 100 m undulator in the LCLS FEL at SLAC). In the last three decades there have been advanced research, studies and applications using short-pulse, high-peak-brightness X-ray radiation produced in storage rings and synchrotrons. Recent developments in this field suggest much more compact, bright and ultra-short pulse X-ray sources based on a laser accelerator and heavy target (U.S. Pat. No. 6,333,966 to Schoen), relativistic electron injector and laser beam (i.e. inversed Compton source, U.S. Pat. No. 6,724,782 to Hartemann et al and U.S. Pat. No. 7,391,850 to Kaertner et al). U.S. Pat. No. 7,379,530 to Hoff et al applies a pair of pulse gamma-sources for detection of nuclear devices within a container but does not disclose how the short gamma-ray pulses are produced.
The history of THz sources is more recent. In particular, compact or small terahertz sources available today operate mostly in the CW mode and deliver very low maximum power not exceeding several watts. Such devices include Gunn diodes, Schottky varactor, IMPATT, TUNNET solid-state diode arrays, solid-state laser on lightly doped p-type germanium mono-crystals, Quantum Cascade Lasers, vacuum electronics devices: orotrons, clinotrons, Smith-Purcell, BWO, TWT, and molecular line-tunable lasers, e.g., CO2-pumped methanol.
Time-domain THz spectroscopy uses two types of pulse terahertz compact sources: electro-optical and photoconductive antennas that provide laser frequency downconversion or optical rectification. These incoherent, broadband sources are pumped with a femtosecond laser and cannot deliver more than a dozen of kW peak power even if an array of thousands of such emitters is used. Short-pulse THz sources based on relativistic electron beams can deliver much higher pulse energies at high maximum power—typically tens of kilowatts from FELs, gyrotrons, synchrotrons and storage rings. However these sources are large and very expensive. Only a few of them can deliver peak power exceeding 100 kW.
Peak power of hundreds of kW in ps-sub-ns range from more compact (than FEL) sources is crucial for the investigation of a large variety of non-linear phenomena and fast processes at THz frequencies. Compactness, easy access, and minimal thermal load that should remain well below 100 mW are also critical for these applications.
Many small laboratories and research groups in government and private sectors conduct research using both X-ray and terahertz radiations and develop corresponding techniques using ultrashort pulses. Currently both of these radiations of high peak intensities are available only at large national facilities with energetic electron beams: coherent synchrotron radiation sources and some linear accelerators equipped with corresponding insertion devices (undulators, bending magnets and wigglers) such as the Advanced Photon Source (APS) at LBNL or the JLAB FEL. These machines are very expensive (>$10 mln for low energy machines with moderate parameters) and are currently confined to government laboratories for basic research applications
Applications of both X- and T-rays include, but are not limited to, protein crystallography; identification and selective modification (e.g., mild-ablation) of DNA, enzymes, proteins and capsides (protective protein shells) of viruses.
Another example of a fused X-T ray application is homeland security: X-ray screening to be added with T-ray screening to enable remote detection of concealed weapons, chemical agents, explosives, and hazardous materials, to detect the presence of toxic or semitoxic gases, and illegal drugs, to uncover hidden objects (e.g. under the clothing) and contraband such as fine art hidden under layers of décor painting.
Other examples of potential application of a combined X-ray and T-ray source are in the fields of medicine and chemistry. Most of these fused applications need compact high-brightness, pulse sources that combine the production of both X-rays and T-rays. Both kinds of radiations should have high peak intensity and brightness, and exhibit low average dose (for X-rays) and heat load (for T-rays).
A compact source for generation of both X-ray and T-ray ultra-short pulses in the same device is also needed in emerging ultrafast technology which has many applications outside its traditional enclaves of time-domain spectroscopy and imaging.